Admission Control Utilizing Backup Links in an Ethernet-Based Access Network

ABSTRACT

An admission control process in an Ethernet-based access network having both active links and idle backup links. When a service request is received in an access node, the process searches for a path of links to an access edge node with sufficient bandwidth to serve the service request. Active links are searched first. If a path of active links with sufficient bandwidth cannot be found, and the service is a unicast request, the process searches for a path that utilizes at least one idle backup link and has sufficient bandwidth to serve the service request.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to communications networks, andin particular, to an admission control process in an Ethernet-basedaccess network.

DESCRIPTION OF RELATED ART

In the communications industry, both operators and customers haverecognized the advantages of triple-play services (i.e., a bundledservice for voice, data, and video services). To provision triple-playservices to end users connected to a broadband access network, awell-defined Quality of Service (QoS) mechanism is essential. QoSsupport can be divided into two categories: absolute QoS and relativeQoS, with both having their proper applications. For services withabsolute QoS support, admission control is needed.

From a high level, an admission control process for an Ethernet basedaccess network can be described as the following:

-   -   Boolean Bandwidth_admission_control (QoS_request, Topology).

This process takes two input parameters, QoS_request and Topology. Thereturn value of the process will be “true” when there is sufficientbandwidth to admit an admission request, or “false” where the requestmust be rejected due to insufficient bandwidth. When checking theavailable bandwidth, the process looks at the source and destination Macaddresses included in the QoS-request parameter, and determines the pathin the network between the source and the destination using theinformation in the Topology parameter.

The Ethernet-based access network may have different topologies, but atany given time, the active links in an Ethernet based access networkalways form a tree structure. This is because when there is an activering in the access network, broadcast traffic will be transmitted againand again along the ring and will eventually flood the network. Sotraditionally, there are a number of backup links in the access networkthat are activated only when an active link fails, which results in anew tree structure. The backup links are usually idle, i.e., they do notshare the traffic load. The bandwidth admission control process onlychecks the active links along the path. Thus under certain conditions,the admission control process may reject an admission request becausethe active links are heavily loaded, while the backup links are idlewithout any traffic load at all. This is a waste of network resources.

Accordingly, there is a need for an improved an admission controlprocess that overcomes the shortcomings of the prior art. The presentinvention provides such a process.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to an admission controlprocess in an access network having both active links and idle backuplinks. The process includes receiving a service request in the accessnetwork, and searching for a path of links with sufficient bandwidth toserve the service request. The searching step includes searching boththe active links and the idle backup links in the access network. Theservice request is admitted if a path with sufficient bandwidth to servethe service request is found. The process may search first for a path ofactive links having sufficient bandwidth to serve the service request,and then search for a path having at least one idle backup link andsufficient bandwidth if a path of active links with sufficient bandwidthis not found.

In another aspect, the present invention is directed to an admissioncontrol process in an Ethernet-based access network having both activelinks and idle backup links. The process includes receiving a servicerequest in the access network; searching for a path of active links withsufficient bandwidth to serve the service request; and if a path ofactive links with sufficient bandwidth to serve the service request isfound, admitting the service request. If a path of active links withsufficient bandwidth to serve the service request is not found, theprocess searches for a path with sufficient bandwidth to serve theservice request among paths having at least one idle backup link. If apath having at least one idle backup link and sufficient bandwidth toserve the service request is not found, the service request is rejected.If a path having at least one idle backup link and sufficient bandwidthto serve the service request is found, the service request is admitted.Paths with idle backup links may be searched only if the service requestis a unicast request.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an exemplary access networktopology suitable for implementing the present invention;

FIG. 2 is a flow chart illustrating an existing access control process;and

FIG. 3 is a flow chart illustrating the steps of a preferred embodimentof the process of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In an Ethernet-based access network, the backup links are idle mainlybecause of the broadcasting traffic. The present invention uses thebackup links to augment the active links when the active links areheavily loaded, thus improving the network performance.

The bandwidth admission control process of the present invention firstfollows the standard admission process to determine whether there isavailable bandwidth on active links along the path to handle a newunicast admission request. If enough bandwidth is found on the activepath, the process returns “true”. However, when there is insufficientbandwidth available on the active path for the unicast request, insteadof returning “false” and rejecting the service request, the presentinvention searches for another path utilizing the backup links. Theinvention searches from the network node attached to the failing link tothe destination node. Several such paths may exist, and the admissioncontrol process checks available bandwidth on all paths, starting withthe path having the least number of hops. If available bandwidth isfound on one of the paths, the admission control process returns “true”and instructs the affecting node to change its forwarding table andswitch follow-up traffics along the newly found path. If no paths arefound with enough bandwidth, or an extra path does not exist, theadmission control process returns “false” and rejects the servicerequest.

FIG. 1 is a simplified block diagram of an exemplary access networktopology 10 suitable for implementing the present invention. In thenetwork, access nodes (AN1-AN6) 11 a-11 f are connected to aggregationnodes (AGN1-AGN3) 12 a-12 c. The aggregation nodes and the access edgenode (AEN) 13 are connected in a fully meshed way. Thus three backuplinks 14 a-14 c, depicted by dotted lines, are provided. Active linkswithin the network are depicted by solid lines. QoS admission requestsare received through the access nodes 11.

The algorithm utilized by the bandwidth admission control process of thepresent invention is as follows:

-   -   Boolean Bandwidth_admission_control (QoS_request, Topology)

There are two input parameters, the QoS_request and Topology. Thedetailed structures of the two parameters are:

QoS_request: ServiceType: Unicast/Multicast/Broadcast; /* The algorithmchecks backup links only for Unicast service */ SourceMacAddress;DestinationMacAddress; /* This address pair is used to find thecorresponding network nodes */ MinBandwidth; PeakBandwidth; /* Thebandwidth requirement of the service */ MaxDelay; MaxJitter; etc /*Other parameters are not considered in this algorithm */ Topology:NodeAddress[1..n]; /* Mac address of each node in the networkLinks[1..m]: /* All links in the network */ EndNode1: NodeAddressEndNode2: NodeAddress /* The addresses of the two nodes to which thelink is connected */ Capacity; /* Total bandwidth */ AvailableCapacity;/* Currently Available Bandwidth */ Status: Active/Backup; /* If thelink is in use or idle */

FIG. 2 is a flow chart illustrating an existing access control process.The process starts at step 21 where a service request is received froman access node. The service request includes a QoS-request parameter. Atstep 22, the process enters the normal admission control process. Theprocess looks at the source and destination Mac addresses included inthe QoS-request parameter, and determines whether the active links alongthe path have sufficient bandwidth to handle the new admission request.The process only checks the active links along the path. If all of thelinks have sufficient bandwidth to handle the new admission request, therequest is admitted. If any of the active links have insufficientbandwidth, the admission request is rejected.

At step 23, it is determined whether bandwidth conditions enable the newadmission request to be admitted. If so, the process moves to step 24and admits the service request. At step 25, the process modifies theavailable capacity for the involved links. The process then ends at step26. However, if it was determined at step 23 that bandwidth conditionsdo not enable the new admission request to be admitted, the processmoves to step 27 where the service request is rejected. The process thenends at step 26.

FIG. 3 is a flow chart illustrating the steps of a preferred embodimentof the process of the present invention. As noted above, the bandwidthadmission control process of the present invention first follows thestandard admission process (steps 21-23) to determine whether there isavailable bandwidth on active links along the path to handle a newadmission request. If enough bandwidth is found on the active path, theprocess admits the new service request at step 24, modifies theavailable capacity for the involved links at step 25, and ends at step26.

However, if it is determined at step 23 that there is insufficientbandwidth to handle the new request, the process moves to step 31 whereit is determined whether the new request is a unicast request. If not,the process moves to step 27 where the service request is rejected. Theprocess then ends at step 26.

However, if the service request is a unitcast request, the process movesto step 32 and searches all paths, including the backup links, for apath with sufficient bandwidth. The invention searches from the networknode attached to the failing link (i.e., the link with insufficientbandwidth) to the destination node. Several such paths may exist, andthe admission control process checks available bandwidth on all paths,starting with the path having the least number of links. At step 33, theprocess individually analyzes each path found. At step 34, the processchecks the bandwidth capacity of each link on a given path. At step 35,it is determined whether the link currently being analyzed hassufficient bandwidth to handle the new request. If not, the processmoves to step 36 and determines whether the path currently beinganalyzed is the last path. If so, then no paths have been found withsufficient bandwidth, or an extra path does not exist. Therefore, theprocess moves to step 37 where the new unicast request is rejected. Theprocess then ends at step 38.

However, if it is determined at step 35 that the link currently beinganalyzed has sufficient bandwidth to handle the new request, the processmoves to step 39 where it is determined whether this link is the lastlink on the path currently being analyzed. If not, the process returnsto step 34 and continues to analyze the remaining links on the analyzedpath until all links have been analyzed or an link with insufficientbandwidth is discovered.

Once all links on a given path have been determined to have sufficientbandwidth, the process moves to step 40 where the unicast request isadmitted. At step 41, the process modifies the available capacity forthe involved links. The process also instructs the affecting node tochange its forwarding table and switch follow-up traffic along the newlyfound path. The process then ends at step 38.

It is clear from FIG. 3 that the heaviest part of the process is tosearch for all available paths between any source and destination pairs.Several steps may be taken to optimize this part of the process. First,since the network topology will not change often, the path, includingall links, can be calculated in advance when the network stabilizes andis stored statically in the system. That way, the searching andcalculation do not have to be performed every time a service requestarrives. This dramatically reduces the resources and time needed for theadmission control. When there is a network topology change, or when linkfailure occurs, all paths are re-calculated again after the networkstabilizes again. Since Ethernet-based access networks are quite stable,such recalculations should be rare.

Another possible optimization lies in the fact that in the accessnetwork, all requests enter the network through the access nodes 11 a-11f and leave the network via the access edge node 13. Therefore, the pathcalculation is only needed between access node/access edge node pairsinstead of all node pairs in the network. This further reduces the timeand resources needed for path calculation.

A third optimization provides improved network performance. After allpaths between a given pair are found, the paths are sorted based on aweighting and are stored in a weight-descendent or ascendant manner. Theweighting may be based on any factor of interest to the operator, suchas number of hops, link capacities, and the like. Thereafter, when theadmission control process searches for an available path for a servicerequest, the process analyzes the more favorable (weighted) path first.

The complexity of the present invention resides heavily in the pathsearching. To search all possible paths between a given pair of aweighted graph, a number of existing algorithms, such as K-Shortest Path(KSP) and Maximum Flow (MF) may be applied. Among them, the KSPalgorithm provides a rather good approximation of finding all possiblepaths. Another advantage of KSP is that its output is already sortedaccording to the pre-defined weight, which saves the sorting time aswell. In the worst case, the admission control process provides acomplexity of O(nlog(n)), where n is the number of nodes in the network.However, the complexity is mitigated if the process is optimized so thatpath searching is not required every time a service request arrives.Additionally, the searching is not required once the network is stable.Given the highly reliable nature of Ethernet-based networks today (over99:9%), the actually complexity the process adds to the system isnegligible.

Thus, the bandwidth admission control process of the present inventionimproves network resource utilization by making use of the backup linksin the network for unicast service requests. The process improvesnetwork performance by enabling additional service requests to beadmitted into the network that would otherwise be rejected using thetraditional bandwidth admission control process. The complexity of thepresent invention does not increase with increasing numbers of services.The complexity remains constant most of the time, and consumesadditional computational power only when the network changes andconverges again.

The present invention may of course, be carried out in other specificways than those herein set forth without departing from the essentialcharacteristics of the invention. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

1. An admission control process in an access network having both activelinks and idle backup links, said process comprising the steps of:receiving a service request in the access network; searching for a pathof links with sufficient bandwidth to serve the service request, saidsearching step including: searching first for a path of active linkshaving sufficient bandwidth to serve the service request; and if a pathof active links with sufficient bandwidth is not found, searching for apath having at least one idle backup link and sufficient bandwidth toserve the service request; and admitting the service request if a pathwith sufficient bandwidth to serve the service request is found.
 2. Theprocess according to claim 1, wherein the access network is anEthernet-based access network.
 3. The process according to claim 1,wherein the step of searching for a path having at least one idle backuplink is performed only if the service request is a unicast request. 4.The process according to claim 1, wherein the access network includes aplurality of access nodes where service requests enter the accessnetwork and an access edge node where service requests exit the accessnetwork, wherein the searching step includes searching only paths thatconnect the access edge node with the access node where the servicerequest enters the network.
 5. The process according to claim 4, furthercomprising, prior to receiving the service request, the steps ofdetermining and storing information regarding all possible paths fromthe plurality of access nodes to the access edge node for a particularnetwork topology, wherein the stored path information is utilized tosearch for paths from the access node where the service request entersthe access network to the access edge node when the service request isreceived.
 6. The process according to claim 5, wherein the steps ofdetermining and storing information regarding all possible paths fromthe plurality of access nodes to the access edge node are performedfollowing a topology change or link failure.
 7. The process according toclaim 5, further comprising sorting and storing the path informationbased on a weighting factor, wherein the searching steps includesearching for a path with sufficient bandwidth beginning first with thepath most favorably weighted.
 8. The process according to claim 7,wherein the weighting factor is operator defined.
 9. The processaccording to claim 8, wherein the weighting factor is based at least onthe number of links in each path and the link capacity of each link. 10.An admission control process in an access network having both activelinks and idle backup links, said process comprising the steps of:receiving a service request in the access network; searching for a pathof active links with sufficient bandwidth to serve the service request;if a path of active links with sufficient bandwidth to serve the servicerequest is found admitting the service request; if a path of activelinks with sufficient bandwidth to serve the service request is notfound: determining whether the service request is a unicast request;rejecting the service request if the service request is not a unicastrequest; and if the service request is a unicast request: searching fora path with sufficient bandwidth to serve the service request amongpaths having at least one idle backup link; if a path having at leastone idle backup link and sufficient bandwidth to serve the servicerequest is not found, rejecting the service request; and if a pathhaving at least one idle backup link and sufficient bandwidth to servethe service request is found, admitting the service request.
 11. Theprocess according to claim 10, wherein the access network is anEthernet-based access network.
 12. The process according to claim 10,wherein the access network includes a plurality of access nodes whereservice requests enter the access network and an access edge node whereservice requests exit the access network, wherein the searching stepsinclude searching only paths that connect the access edge node with theaccess node where the service request enters the network.
 13. Theprocess according to claim 12, further comprising, prior to receivingthe service request, the steps of determining and storing informationregarding all possible paths from the plurality of access nodes to theaccess edge node for a particular network topology, wherein the storedpath information is utilized to search for paths from the access nodewhere the service request enters the access network to the access edgenode when the service request is received.
 14. The process according toclaim 13, wherein the steps of determining and storing informationregarding all possible paths from the plurality of access nodes to theaccess edge node are performed following a topology change or linkfailure.
 15. The process according to claim 13, further comprisingsorting and storing the path information based on a weighting factor,wherein the searching steps include searching for a path with sufficientbandwidth beginning first with the path most favorably weighted.
 16. Theprocess according to claim 15, wherein the weighting factor is operatordefined.
 17. The process according to claim 16, wherein the weightingfactor is based at least on the number of links in each path and thelink capacity of each link.
 18. An admission control system in an accessnetwork having both active links and idle backup links, said systemcomprising: an access node for receiving a service request in the accessnetwork; means for searching for a path of links between the access nodeand an access edge node having sufficient bandwidth to serve the servicerequest, said searching means including: means for searching first for apath of active links having sufficient bandwidth to serve the servicerequest; and means, responsive to a determination that a path of activelinks with sufficient bandwidth is not found, for searching for a pathhaving at least one idle backup link and sufficient bandwidth to servethe service request; and means for admitting the service request if apath with sufficient bandwidth to serve the service request is found.